1. Field of the Invention
The present invention relates to generating random signals, and more particularly, to a random signal generator, a random number generator including the random signal generator, and a method of generating a random signal.
2. Description of the Related Art
Generally, secure data communications, involving a smart card, for example, may require an encrypted key for protecting user information. Random numbers are typically used to generate the encrypted key. A random number may be classified as a pseudo random number or a physical random number.
A pseudo random number is generated artificially by logic circuits and software programs. For example, the pseudo random number may be generated using a Rivest-Shamir-Adelman (RSA) cryptoalgorithm and an elliptic curve cryptosystem. However, the pseudo random number has a deterministic sequence, which may be anticipated by a hacker if an initial condition of the pseudo random number system is revealed.
A physical random number, also referred to as a true random number, may be generated based on a physical phenomenon that exists in the natural world. Thermal noise of a resistor, short noise of a PN junction of a semiconductor and radioactive waves are examples of such a physical phenomenon. Because the physical phenomenon cannot be predicted, the physical random number is more appropriate for protecting private information. However, noise intensity of the underlying physical phenomenon on which the random number is based is typically small, and thus a high voltage is required to convert the small noise to a random number. Consequently, many difficulties arise in attempting to apply a physical random number to a large-scale integrated circuit (LSI), for example.
An example of a random number generator circuit using thermal noise is described in HOLMAN et al., “An Integrated Analog/Digital Random Noise Source,” IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS: FUNDAMENTAL THEORY AND APPLICATIONS, Vol. 44, No. 6 (June 1997). In the random number generator circuit, a resistor for generating thermal noise is coupled to both sides of an amplifier. In addition, the random number generator circuit includes a structure for comparing an output of the amplifier and a reference voltage. As the random number generator circuit uses the resistor as a feedback device, an output impedance of the amplifier must be considerably small. Therefore, the disclosed random number generator circuit is not appropriate for complementary metal oxide semiconductor (CMOS) processes, for example, because of increased size and power consumption of the circuit.
When the amplifier of a conventional random number generator circuit has a voltage offset, the operation of the amplifier runs off a saturation region. Therefore, sufficient voltage gain may not be acquired. In addition, when a source voltage and/or a ground voltage fed to the random number generator circuit includes noise, the randomness of the generated sequences may be degraded. When a low drop output (LDO) regulator is included to stabilize a power supply voltage, the structure of the random number generator circuit becomes more complex. Further, the LDO may not adequately address problems associated with noise in the ground voltage.